Keep in mind that these transmissions were used mainly for cost reduction and also that the vehicles they were used in had lower HP/TQ ratings than those that used the Muncie.
I'll let you draw your own conclusion considering the above info.
Also see- http://www.chevelles.com/forums/show...90#post3501090

When I first bought my 70 BBC it had the T-10.....went to a Muncie M-21. Has runs very well now. I did not have the HP in the car with the T-10 that I have now. I would recommend the Muncie over the T-10.

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